This invention relates to a respiration-time control device in a respirator for infants in which the control valve is switched with the aid of a pressure-sensitive control means.
Respirators for infants have to comply with particular requirements. Thus, a relatively small respiration volume must be supplied at a frequency as high as possible and under exactly controlled conditions, and a high dead space ventilation must be avoided. The time control device for controlling the operations of the respiration cycle has to work with a corresponding accuracy.
In a known respirator for infants, breathing air is supplied to the patient, during the inspiration phase, under the control of a switch valve and, during the expiration phase, the air is evacuated. The respiration frequency is adjustable and the ratio of inspiration time to expiration time can be chosen. For inspiration, the switch valve opens the supply line conducting breathing gas to the patient and, for expiration, this line is shut off and the expiration line is opened instead. The supply line comprises a relief valve preventing an excessive peak pressure. The time control of the switch valve is effected by means of an electronic oscillator adapted for the adjustment both of the frequency and the ratio of the inspiration time to the expiration time. The time control device works electronically. This is disadvantageous since, due to the composition of two sorts of energy, namely electricity and pressure gas, the apparatus is complicated and not simple in use (Loosco prospectus No. 681 008).
Another known respirator for infants permits spontaneous respiration and time-controlled respiration in a purely pneumatic way. In both cases, the breathing gas flows continuously in the supply line in the direction of the patient and then, through the expiration line and the expiration valve, to the outsie. Close to the patient, the two lines are united in a connection piece wherefrom only one conduit leads to the user. During the spontaneous respiration, the patient takes the breathing gas from the flowing stream and exhales it again into the flowing stream. The patient determines the respiration phases and respiration frequencies. The counterpressure in the breathing gas stream is small and is overcome.
During time-controlled respiration, the sequence of the respiration phases is determined by the opening and closing of the expiration valve. With the expiration valve closed, the full breathing gas stream flows to the patient. The expiration phase is started by the opening of the expiration valve. Then the breathing gas stream, in which the exhalation stream is admixed in the connection piece, flows past the patient to the expiration valve. The time control device, for assuring actuation of the expiration valve at the right instants, comprises a plurality of systems of pneumatic component parts. This very circumstance is the drawback of the respirator. It is difficult to exactly control the different systems which, in addition, are interdependent in their operation. Only an accurate adjustment of all of the elements and their continuous checking can ensure the desired values of the respiration frequency and the ratio of the inspiration time to the expiration time. The adjustment and securing of the control during the respiration is made particularly difficult in the treatment of infants by the required small respiration volume at a high respiration frequency (Babybird-Ventilator-Bird-Corporation 1972, Form 5900.2).
In another proposed respirator, the respiration phases are controlled, both in time and spontaneously, by the patient. By pressure signals furnished by a control device, a gas-pressure-controlled valve is opened and closed. In the inspiration phase, the breathing gas flows through the opened valve to the patient. Pressure controlled by the patient himself or in accordance with the adjusted time, the valve closes and terminates the inspiration phase. The expiration air flows to the outside along a separate path. The control device, both for the time-controlled respiration and the spontaneous respiration, is a pressure-controlled control means comprising an actual-value pointer whose range of deflection is limited by a displaceable air barrier at each side, where the pointer, upon entering, interrupts a continuously flowing control stream and thereby furnishes a pressure signal. However, this respirator cannot be used for infants without further provisions.